1. Field of the Invention
This invention relates to new and useful improvements in pigment dispersions. It relates particularly to the transfer of a pigment from an aqueous pulp directly into organic vehicles by an operation known to those skilled in the art as flushing.
2. Description of the Prior Art
Historically, organic pigments have been made by coupling in a dilute aqueous slurry, which is then filtered in a filter press to concentrate the pigment. The presscake is either dried to obtain a dry color, or "flushed" to transfer the pigment particles from the aqueous phase to a non-polar oil or resin phase. This assists in keeping pigment particles non-agglomerated and easier to dilute for ultimate use in inks or coatings. Flushing has been carried out for many decades by mixing pigment presscake with suitable types and quantities of "vehicles" which may be an oil, or a solution of resin or resins and other additives in a solvent. In the prior art, the transfer was effected by merely kneading the presscake and vehicle together until substantially all the water has separated. There were generally batch-type operations employing sigma-blade mixers similar to dough mixers or Banbury mixers. Such processes are very energy intensive and labor intensive since the flushers have to be tilted to remove water from time to time as it breaks, i.e., becomes freed of pigment which has transferred to the oil phase. Also, the final paste or dispersion is often extremely viscous and must be removed manually by shoveling and scraping with hoes and other suitable manual tools.
Accordingly, it is a purpose of the instant invention to provide for flushing a pigment which may be carried out continuously and completely automatically.